ASM Hacking | Overlay not loading in game when changing more than 1 byte in the overlay.

Hi, I'm currently working on trying to do ASM Hacking on a game, Professor Layton and Pandora's box to be exact. I've been trying hard to get this to work. The NSMBE ASM Patcher didn't work, so I wrote my own in python with the use of the ndspy library, and I so far have been able to do hooks in arm9.bin, but since most of the interesting code is put in the overlays, I was working on being able to hook to overlays.
The thing is though, whenever I try to modify the uncompressed overlay. When...

ASM Hacking | Overlay not loading in game when changing more than 1 byte in the overlay.